As an image display device substitutable for liquid crystal display (LCD), image display devices with the use of technology such as an electrophoresis method, an electro-chromic method, a thermal method, dichroic-particles-rotary method are proposed. As for these image display device, it is conceivable as inexpensive visual display device of the next generation from a merit having wide field of vision close to normal printed matter, having smaller consumption with LCD, spreading out to a display for portable device, and an electronic paper is expected.
Recently, electrophoresis method is proposed that microencapsulate dispersion liquid made up with dispersion particles and coloration solution and dispose the liquid between faced substrates. However, in the electrophoresis method, there is a problem that a response rate is slow by the reason of viscosity resistance because the particles migrate among the electrophoresis solution. Further, there is a problem of lacking imaging repetition stability, because particles with high specific gravity of titanium oxide is scattered within solution of low specific gravity, it is easy to subside, difficult to maintain a stability of dispersion state. Even in the case of microencapsulating, cell size is diminished to a microcapsule level in order to make it hard to appear, however, an essential problem was not overcome at all.
Besides the electrophoresis method using behavior in the solution, recently, a method wherein electro-conductive particles and a charge transport layer are installed in a part of the substrate without using solution is proposed. [The Imaging Society of Japan “Japan Hardcopy '99” (Jul. 21–23, 1999) Transaction Pages 249–252] However, the structure becomes complicated because the charge transport layer and further a charge generation layer are to be arranged. In addition, it is difficult to constantly dissipate charges from the electro-conductive particles, and thus there is a drawback on the lack of stability.
In order to solve the problems mentioned above, as an image display device enabling rapid response due to a dry-type device, simple construction, inexpensive cost and excellent stability, it is known a dry-type image display device which comprises an image display panel, in which two groups of particles or liquid powders having different colors and different charge characteristics are sealed between a transparent substrate and an opposed substrate, and, in which the particles or the liquid powders, to which an electrostatic field produced by two electrodes having different potentials is applied, are made to move so as to display an image. In the image display device, image display elements are formed by arranging partition walls between the transparent substrate and the opposed substrate.
However, the following tasks arise.
<Tasks of a First Aspect of the Invention>
In the dry-type image display device mentioned above, there is an advantage such that a particle moving resistance is small and a response speed is rapid with respect to the electrophoresis method. A theory of the image display on the dry-type image display device mentioned above is that a pattern is recognized by obtaining a contrast of respective particles. Therefore, it is important to control a luminance factor of white particles, which are a base for reflecting a light. Generally, the white particles are produced by mixing fine particles made of a material having high refraction index into a material having low refraction index. In this case, if the number of the white particles is small. An opacifying rate becomes insufficient, and thus there is a limit for an achievable luminance factor.
<Tasks of a Second Aspect of the Invention>
In the dry-type image display panel mentioned above, there occurs a phenomenon such that the sealed particles do not move after a repetition use because of particle adhesions with each other. Therefore, there occurs a problem such that an image contrast is deteriorated, and thus a durability after the repetition use is insufficient.
<Tasks of a Third Aspect of the Invention>
In the dry-type image display panel mentioned above, as a particle behavior between the substrates each having an actual electrode, it is a common phenomenon that all the particles having the same charge characteristics are not adhered evenly to one electrode surface but they sometimes generate an agglutinated cluster between the substrates. In this case, the number of the particles adhered to a display electrode surface becomes small, and thus there occurs a problem such that a display performance is extremely deteriorated.
In the case of the agglutinated cluster generated by the particles having different charge characteristics, it is relatively easy to crush the agglutinated cluster by making an electric field intensity larger, since the agglutination occurs due to Coulomb's force etc. between two particles. However, it is difficult to crush the agglutinated cluster in the same manner if the agglutinated cluster is formed by the particles having the same charge characteristics. In this case, it is not possible to crush the agglutinated cluster by en external electronic stress, and thus a solving method is not certain.
<Tasks of the Fourth Aspect of the Invention>
In the dry-type image display device mentioned above, there is an advantage such that a particle moving resistance is small and a response speed is rapid with respect to the electrophoresis method. A theory of the image display on the dry-type image display device mentioned above is that a pattern is recognized by obtaining a contrast of respective particles. Therefore, it is important to control a color of the white particles which are a base for emitting a color.
Heretofore, as coloring particles such as white particles and so on, use is made of: crushed particles obtained by mixing pigment and dye into a polymer and crushing/classifying the mixed polymer; polymerized particles obtained by involving the pigment and dye by means of a polymerization method such as suspension polymerization, emulsification polymerization and seed polymerization and so on; and composite particles in which the pigment and dye and so on are adhered to a surface of mother particles. However, in the crushed particles, there are problems: such that a desired color is not obtained since a particle shape is varied and there is a limit for filling amounts of the pigment and dye; and such that the particles have a damage such that a crack generation and so on when crushed. Moreover, in the polymerized particles, there is a problem such that filling amounts of the pigment and dye become further smaller and thus a desired color is not obtained. Further, in the composite particles, there are problems: such that a coloring is insufficient since the pigment and dye are not existent in the mother particles; such that the pigment and dye are easily picked away from the surface; and such that manufacturing processes are made larger.
<Tasks of a Fifth Aspect of the Invention>
In the dry-type image display panel mentioned above, there occurs a phenomenon such that the sealed particles do not move after a repetition use because of particle adhesions with each other. Therefore, there occurs a problem such that an image contrast is deteriorated, and thus a durability after the repetition use is insufficient.
<Tasks of a Sixth Aspect of the Invention>
In the dry-type image display device mentioned above, there is an advantage such that a particle moving resistance is small and a response speed is rapid with respect to the electrophoresis method. A theory of the image display on the dry-type image display device mentioned above is that a pattern is recognized by obtaining a contrast of respective particles. Therefore, it is important to control a color of the white particles which are a base for emitting a color.
Heretofore, the white particles mentioned above are manufactured by filling white pigment such as titanium oxide (TiO2), zinc oxide, zirconium oxide and so on into a base resin. As a manufacturing method, use is made of a polymerization method and a mixing/crushing method. In the mixing/crushing method, a larger amount of the pigment such as titanium oxide can be added, and thus an excellent whiteness can be obtained. As a shape, circular particles can be obtained in the polymerization method, but the particles have an indefinite shape in the mixing/crushing method. As filling amounts of the white pigment, 50 parts by weight of the white pigment is maximum in the polymerization method with respect to 100 parts by weight of the base resin, but it is possible to fill about 300 parts by weight of the white pigment in the mixing/crushing method with respect to 100 parts by weight of the base resin. As mentioned above, the polymerization method and the mixing/crushing method have good and bad points respectively, but the mixing/crushing method is preferably used from a viewpoint of the most important whiteness.
However, in the mixing/crushing method, if titanium oxide is added more and more to a high extent, a scattering becomes insufficient and thus there is a problem such that a white refraction index decreases. For example, the whiteness becomes maximum at about 200 parts by weight of titanium oxide with respect to 100 parts by weight of the base resin. Then, if titanium oxide is added over 300 parts by weight, it is difficult to perform a mixing process and the white refraction index also decreases. Particularly, in the case of using titanium oxide, there is a problem such that it is difficult to fill over 300 parts by weight of titanium oxide with respect to 100 parts by weight of the base resin.
<Tasks of a Seventh Aspect of the Invention>
As one example of the particles used in the image display device comprising the dry-type image display panel, heretofore, there is a case such that use is made of the particles obtained by: melting pigment, charge control agents and so on with respect to a base resin made of a thermoplastic resin such as polycarbonate (PC) and so on; and mixing/crushing the melted base resin. The particles obtained by the mixing/crushing method using the thermoplastic resin as the base resin in the manner mentioned above have a low heat resistance. Therefore, there is a problem such that the particles are melted and thus adhered/agglutinated to the image display panel during the use of the image display panel under a high temperature or during the works under a high temperature such as a substrate stacking process of the image display panel.
<Tasks of an Eighth Aspect of the Invention>
In the dry-type image display panel mentioned above, an image contrast is not still sufficient, and there occurs a phenomenon such that the sealed particles do not move after a repetition use because of particle adhesions with each other. Therefore, there occurs a problem such that an image contrast is deteriorated, and thus a durability after the repetition use is insufficient.
<Tasks of a Ninth Aspect of the Invention>
In the dry-type image display panel mentioned above, an image contrast is not still sufficient, and there occurs a phenomenon such that the sealed particles do not move after a repetition use because of particle adhesions with each other. Therefore, there occurs a problem such that an image contrast is deteriorated, and thus a durability after the repetition use is insufficient.
<Tasks of a Tenth Aspect of the Invention>
Heretofore, it is not possible to control charge characteristics (positive charge performance and negative charge performance) of a particle material constituting image display media using the image display device having the dry-type image display panel, and the charge characteristics are a value inherent from a resin material constituting the image display media itself.